With only 39 days until the winter Olympic Games in Russia, today's suicide-bomber attack at a train station has some questioning whether the nation is ready to host the international event. NBC's Jim Maceda reports.

By Albina Kovalyova, Producer, NBC News

MOSCOW — At least 16 people were killed in a terror attack by a suspected female suicide bomber at a railway station in Russia Sunday, officials said — the second deadly attack in three days as the country prepares to host the Winter Olympics.

The National Anti-Terrorist Committee said the explosion, at the central railway station in the city of Volgograd, was an act of terror and that a criminal investigation has been launched.

"People were lying on the ground, screaming and calling for help," witness Alexander Koblyakov told Rossiya-24 TV. "I helped carry out a police officer whose head and face were covered in blood. He couldn't speak."

The Russian Investigative Committee, the primary federal investigative agency in the country, said that 10 of the dead had been identified as seven men and three women.

Officials said about 50 additional victims were injured by the bombing in the city formerly known as Stalingrad.

Late Sunday, the IC said that there was a possibility that the bomber was a man, although they believe it was a woman.

"According to the existing information, the explosion was activated by a female terrorist suicide bomber, which got nervous when she got close to the metal detector, and saw a policeman," the IC said on its website. "The investigation is also looking into the possibility that the explosion was caused by a man."

The attack, which happened at about 1 p.m. local time (4 a.m. ET), heightens concern about terrorism ahead of February's Olympics in the Black Sea resort of Sochi, and following similar bombings.

On Friday, a car bomb killed three people in the southern Russian city of Pyatigorsk, 170 miles east of Sochi. In October, another female suicide bomber was blamed for a bus explosion in Volgograd that killed five people.

Gennady Gulyaev / Kommersant Photo via Getty Images

Authorities stand outside the Volgograd train station, where a suspected suicide bomber killed more than a dozen people, on Dec. 29, in Volgograd, Russia.

President Vladimir Putin ordered law enforcement agencies to take all necessary precautions to ensure security, his spokesman

The National Anti-Terrorist Committee said preliminary findings after Sunday's blast showed that the suspect was female, but federal security services were still investigating.

"Today at around 1300 (1 p.m.) an unconfirmed explosive device was detonated in front of the metal detector at the entrance to the train station in Volgograd,” the Committee said on its website. “The preliminary findings show that it was activated by a female suicide bomber."

Andrei Soldatov, a Russian security analyst and investigative journalist, said the attack might have been an attempt to distract authorities from keeping Sochi safe.

“There is no reason to hit Volgograd,” he told NBC News. “Now the authorities have to pay extra attention to Volgograd, they will have to split their attention.

“This tactic worked before. Prior to the Beslan school siege there were two explosions of planes and one in the Moscow metro - it was done especially to distract attention, so the terrorists could prepare the big act.”

In Washington, D.C., a senior administration official gave NBC News a statement from the White House which condemned the attacks, and said "Our hearts go out to the victims and their families."

U.S. counter-terrorism officials said that it was too early to give any good assessment on the attack beyond the basic facts — although one senior official did expect very close cooperation between American agencies and Russian investigators on the case.

NBC News' Alastair Jamieson, in London, Robert Windrem and Hasani Gittens in New York, and Reuters contributed to this report.